The present invention relates to a heat analyzing apparatus for measuring how a material property changes with temperature. More specifically, the invention relates to a differential scanning calorimeter of a heat flux type for measuring a differential heat flow excessively dissipated from and absorbed by a sample as compared to a reference substance based on a temperature difference (differential heat) between the sample and the reference substance.
The conventionally used heat flux type differential scanning calorimeter has a detector structure of the type shown in FIG. 2 and FIG. 3.
The type of FIG. 2 has a detector in a flat plate form soldered to side surfaces of a heating oven formed of a thermally good conductor having a sectional H-character form. The heat flow path within the detector is in a two dimensional form directed radially inwardly from the heat oven side surfaces to a sample section and a reference section.
The type of FIG. 3 has a detector directly placed on a bottom plate of a heat oven formed of a thermally good conductor in a sectional H-character form, as seen in JP-A-60-64250U. The heat flow path within the detector is provided with a neck portion to suppress temperature distribution. The heat flows one-dimensionally to the sample section and the reference section.
In both the types of FIG. 2 and FIG. 3, the heat oven temperature is based on negative feedback control by a program temperature controller, and is accurately controlled linearly with respect to time according to a ramp function. At this time, since the temperature difference between the sample section and the reference section is proportional to a difference in flow of the heat absorbed by or dissipated from them, when multiplied by a proper coefficient, it is regarded as an output of a differential heat flow. In this manner, one type of the differential scanning calorimeter that has a temperature difference output multiplied by a proper coefficient into rating to be dealt with as an output of a differential heat flow is called a heat flux type differential scanning calorimeter.
In the differential scanning calorimeter of the FIG. 2 type, there is a tendency to cause in the heat oven side surfaces a temperature distribution in a direction of A of FIG. 2. In such a case, in the detector directly fixed to the heat oven side surfaces, a temperature difference appear between the sample section and the reference section even in a state that no sample is placed. Due to this, a differential heat flow signal is varied to result in a defect that the accuracy in measurement lowers.
Also, it is unavoidable for the detector to suffer exhaustion such as deterioration due to contamination caused by sample decomposition or exposure to high temperature. However, the detector is soldered to the heat oven side surfaces and difficult to be removed. There has been a necessity to replace the detector in accordance with its exhaustion together with a heat oven having its life still left.
On the other hand, the differential scanning calorimeter of the FIG. 3 type has been proposed in order to solve the above-described problem. However, because the heat flow path is one dimensionally, the efficiency of heat transfer is worse as compared to the two-dimensional structure in the FIG. 2 type. As a result, the time constant in heat flow detection increased, thereby lowering the detector response.
Furthermore, in both the FIG. 2 and FIG. 3 differential scanning calorimeter types, the heat oven of a good heat conductor in the sectional H-character form and the detector are directly soldered or contacted. As a result, it is difficult to avoid fine temperature vibration in the heat oven due to temperature control from vibrating the detector. Due to this, the differential scanning signal is readily ridden on by vibratory noise which results in a reduction or signal sensitivity.
In order to solve the above problem, the present invention is provided with a heating oven with a bottom plate having a cylindrical internal space, a heat buffer plate fixed on the bottom plate and formed of a material having a low heat conductivity, and a differential heat flow detector fixed on the heat buffer plate. The differential heat flow detector is fixed on the buffer plate by screw fastening, and can be mounted/dismounted and replaced if the screws are removed. Also, the differential heat flow detector is structured in a form that a heat conducting metal plate in a flat plate form is held by a heat conducting plate support member made of a thermally good conductor. A differential heat flow signal is outputted as a voltage between metal wires welded to the heat conducting plate. Further, the heat conducting metal plate is soldered at oval or elliptical formed peripheral end portion to the heat conducting plate support member. A pair of convex portions are formed in a longer axis direction. of the oval or elliptical of the heat conducting metal plate and in symmetrical position about a center thereof.
When the temperature of the heating oven is controlled according to a ramp function, one part of the heat flows through the heat buffer plate to the differential heat flow detector in a state that fine thermal vibration is filtered. In the differential heat flow detector, the heat conducting plate support member made of a thermally good conductor functions as a heat sink. Because a difference in heat which flows from the heat sink to a sample section and a reference section composing the pair of convex portions in the heat conducting metal plate is measured by a differential thermocouple formed between the heat conducting metal plate and the metal wire, thus functioning as a differential scanning calorimeter.